Age determination of squid using the gladius

Relatively thin cross- and longitudinal sections (20-40) of squid gladii were made with new histological techniques. A study of the inner structure of these sections shows that an oegopsid gladius (as well as all mollusc shells) is composed in principle of three shell layers: hypostracum, ostracum and periostracum. Each layer consists of numerous thin elementary strata that are shown to be daily growth marks. Thus, the gladius may be used as a recording structure with three independent scales for counting: the three shell layers. The important peculiarity of the gladius as a recording structure is in the equality of its length to the mantle length during the entire life-time. This feature presents us the unique possibility to reconstruct the individual growth of squids day by day, as well as to estimate their age.